Na free sea water

Does anyone have a recipe for sodium free synthetic sea water?
I would like to do some classic fertilization demonstrations using sea
erchins.
If so, please e-mail
Thanks in advance.
I would gladly pay you tuesday for a homebrew today!
Bob McNulty
Department of Biological Sciences
California State University, Chico
BMCNULTY at OAVAX.CSUCHICO.EDU